Removes an annotation from the page with its pop-up, the replies to it (IRT) on the page and their pop-ups, and the
structure tree's references to each; a pop-up removed on its own is removed from its parent's Popup.
public void RemoveAnnotation(PdfAnnotation annotation)
One of Annotations.
ISO 32000-2 §12.5.2 (Annots), §12.5.6.2 (Popup, IRT), §12.5.6.14, and §14.7.5.3 and §14.7.5.4 (object
references and the parent tree). Only the page's Annots array (or the page, when it lists none of its own), the parent
of a removed pop-up and the structure tree change, so an incremental save writes just those; the removed dictionaries stay
in the file, unreferenced.